Diamond substrate and diamond substrate manufacturing method

ABSTRACT

A diamond substrate is formed of diamond single crystals by preparing a base substrate; forming plural pillar-shaped diamonds formed of diamond single crystals on one side of the base substrate; causing a diamond single crystal to grow from a tip of each pillar-shaped diamond and coalescing the diamond single crystals growing from the tips of the pillar-shaped diamonds to form a diamond substrate layer; separating the diamond substrate layer from the base substrate; and manufacturing a diamond substrate from the diamond substrate layer, a shape in an in-plane direction of the diamond substrate is a circular shape or a circular shape having an orientation flat plane formed therein and has a diameter of two inches or more.

TECHNICAL FIELD

The present invention relates to a diamond substrate and a diamondsubstrate manufacturing method.

BACKGROUND ART

A diamond is expected to be an ultimate semiconductor substrate. This isbecause a diamond has a lot of excellent characteristics, which areunparalleled in anywhere as a semiconductor material, such as highthermal conductivity, high electron/hole mobility, high dielectricbreakdown field strength, low dielectric loss, and a wide bandgap. Thebandgap thereof is about 5.5 eV which is a very high value in existingsemiconductor materials. Particularly, in recent years, UV lightemitting elements using a wide bandgap, field effect transistors havingexcellent high-frequency characteristics, and the like have beendeveloped.

When it is considered that a diamond is used as a semiconductor, acertain size such as a diameter of several inches is required. This isbecause when a processing device which is used for micro-machining of ageneral semiconductor such as Si is applied to a diamond, it isdifficult to apply the processing device to a small substrate less thanseveral inches.

Several ideas have been proposed as the method of causing a diamondhaving a certain size to grow. Among the methods, a diamond singlecrystal growing method (so-called mosaic growth method; for example, seePatent Literature 1) of arranging plural small diamond single crystalsubstrates or a manufacturing method (for example, see Patent Literature2) of using a single-crystal magnesium oxide (MgO) substrate as a basesubstrate and forming a diamond film on the base substrate by aheteroepitaxial growth method can be used as a strong candidate.

The mosaic growth method is a technique of growing and forming a largediamond single crystal substrate by arranging plural diamond singlecrystal substrates in a shape of tiles and causing diamond singlecrystals to newly grow on the diamond single crystal substrates using ahomoepitaxial growth method. However, coupling boundaries are formed asareas in which crystal quality deteriorates on the boundaries betweenthe diamond single crystal substrates arranged in the shape of tiles.Accordingly, a coupling boundary is necessarily formed in diamond singlecrystals obtained using the mosaic growth method.

The reason of formation of the coupling boundary is that diamond singlecrystals grow randomly in the area of the coupling boundary, coalescenceoccurs from various directions, and a large amount of potential isgenerated in the coupling boundary. The coupling boundary is a distinctboundary line which can be observed visually.

Since the part of the coupling boundary cannot be used for growth of asemiconductor device, an area which can be used in practice is limitedwith respect to the area of the diamond single crystal substrate whichis obtained by the mosaic growth method.

To make matters worse, the area of the diamond single crystal substratewhich can be used to manufacture a semiconductor device does not matchthe size of a semiconductor device chip necessarily. Accordingly, in theprocess of manufacturing a semiconductor device in the diamond singlecrystal substrate, it is necessary to perform the process to avoid thecoupling boundary. As a result, the process of manufacturing asemiconductor device is complicated.

On the other hand, the heteroepitaxial growth method is a technique ofcausing a diamond film which will be a diamond substrate toepitaxial-grow on a base substrate formed of a material having differentphysical properties. Since one diamond film epitaxial-grows on one basesubstrate, there is no concern that a coupling boundary between pluraldiamond single crystal substrates is formed like the mosaic growthmethod.

Accordingly, among the two methods of the mosaic growth method and theheteroepitaxial growth method, the heteroepitaxial growth method isparticularly prospective in that a substrate area in which asemiconductor device can be manufactured is not easily restricted.

However, a stress is generated in crystals of a diamond substrate formedby growth due to a difference in lattice constant and thermal expansioncoefficient between the base substrate and the diamond and thus a warpor a crack is generated in the diamond substrate. Accordingly, it is noteasy to obtain a large substrate using the heteroepitaxial growthmethod.

Therefore, several prior arts relevant to a decrease in stress generatedin a diamond formed by the heteroepitaxial growth method have beenreported (for example, see Patent Literature 3).

Patent Literature 1: Japanese Patent No. 3387154

Patent Literature 2: Japanese Patent No. 5066651

Patent Literature 3: Japanese Unexamined Patent Application Laid-openNo. 2007-287771

DISCLOSURE OF THE INVENTION Technical Problem

However, although ten years or more passes after the above-mentionedprior arts have been reported, diamond substrates which have beenmanufactured using the heteroepitaxial growth method have a maximumdiameter of 1.5 inches and a substrate of two inches or more which isrequired for application to semiconductor has not been manufactured yet.In consideration of this point, the prior arts have not basically solvedthe problem about relaxation of a stress in diamond crystals grown inthe heteroepitaxial growth method. That is, a decrease in warp or crackin a diamond substrate of two inches or more has not been realized, andthe upper-limit diameter of the diamond substrates having the decreasedwarp or crack is kept 1.5 inches.

This situation can be theoretically described using Expression 1.Expression 1 indicates that a warp 8 of a diamond substrate increases bya variation of a square of a diameter I with an increase in diameter Iof the diamond substrate. Accordingly, with an increase in diameter I ofa diamond substrate, a stress a generated in diamond crystals increases.For this reason, the prior arts have a limit in suppressing a stress indiamond crystals and only diamond substrates having a diameter up toabout 1.5 inches have been reported as realizable examples. InExpression 1, E denotes a Young's modulus, υ denotes a Poisson's ratio,b denotes a thickness of a base substrate, and d denotes a thickness ofa diamond substrate.

$\begin{matrix}{\sigma = \frac{E\; b^{2}\delta}{3\left( {1 - \upsilon} \right)I^{2}d}} & {{Expression}\mspace{14mu} 1}\end{matrix}$

The present invention is made in consideration of the above-mentionedcircumstances and an object thereof is to provide a large diamondsubstrate with a diameter of two inches or more.

Another object of the present invention is to provide a diamondsubstrate manufacturing method which can manufacture a large diamondsubstrate with a diameter of two inches or more

Technical Solution

The above-mentioned objects are achieved by the following presentinvention. That is, a diamond substrate according to the presentinvention is formed of diamond single crystals, and a shape in anin-plane direction of the diamond substrate is a circular shape or acircular shape having an orientation flat plane formed therein and has adiameter of two inches or more.

A diamond substrate manufacturing method according to the presentinvention includes: preparing a base substrate; forming a plurality ofpillar-shaped diamonds formed of diamond single crystals on one side ofthe base substrate; causing a diamond single crystal to grow from a tipof each pillar-shaped diamond and coalescing the diamond single crystalsgrowing from the tips of the pillar-shaped diamonds to form a diamondsubstrate layer; separating the diamond substrate layer from the basesubstrate; and manufacturing a diamond substrate from the diamondsubstrate layer, wherein a shape in an in-plane direction of the diamondsubstrate is a circular shape or a circular shape having an orientationflat plane formed therein and has a diameter of two inches or more.

Advantageous Effects

According to the diamond substrate of the present invention, it ispossible to realize a large diamond substrate with a diameter of twoinches or more which is formed of diamond single crystals.

According to the diamond substrate manufacturing method of the presentinvention, the diamond single crystals growing from the pillar-shapeddiamonds are coalesced to manufacture a diamond substrate layer.Accordingly, by increasing the number of pillar-shaped diamonds, it ispossible to easily manufacturing a large-diameter diamond substratelayer with a diameter of two inches or more.

According to the diamond substrate manufacturing method of the presentinvention, a stress is generated in each pillar-shaped diamond due to adifference in lattice constant and/or a difference in thermal expansioncoefficient between the base substrate and the diamond substrate layerwhen the diamond substrate layer is grown, and the pillar-shapeddiamonds are destroyed by the stress to separate the diamond substratelayer from the base substrate.

Accordingly, even when a stress generated in the diamond substrate layerincreases with an increase in size, the stress of the diamond substratelayer is released toward the outside by destruction of the pillar-shapeddiamonds and thus formation of a crack in the diamond substrate layer isprevented. In this respect, it is also possible to manufacture a largediamond substrate.

By manufacturing the diamond substrate from the diamond substrate layer,it is possible to manufacture a large-diameter diamond substrate with adiameter of two inches or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an example of a diamondsubstrate according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a base substrate according tothe embodiment.

FIG. 3 is a schematic diagram illustrating a state of the base substratewith a diamond layer according to the embodiment.

FIG. 4 is a schematic diagram illustrating the base substrate havingplural pillar-shaped diamonds formed thereon.

FIG. 5 is a perspective view illustrating the base substrate havingplural pillar-shaped diamonds formed thereon.

FIG. 6 is a schematic diagram illustrating the base substrate withpillar-shaped diamonds having a diamond substrate layer formed thereon.

FIG. 7 is a perspective view illustrating the base substrate withpillar-shaped diamonds having a diamond substrate layer formed thereon.

FIG. 8 is a schematic diagram illustrating the diamond substrate layer,the base substrate, and the pillar-shaped diamonds which warp in aconvex shape due to a tensile stress.

FIG. 9 is a schematic diagram illustrating a state in which thepillar-shaped diamonds are destroyed and the diamond substrate layer isseparated from the base substrate.

FIG. 10 is a schematic diagram illustrating another example of the basesubstrate having plural pillar-shaped diamonds formed thereon.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a diamond substrate according to the present invention willbe described in detail with reference to FIG. 1. The shape in anin-plane direction of the diamond substrate according to the presentinvention is not particularly limited and may be, for example, arectangular shape. However, a circular shape can be preferably used fromthe viewpoint of easy use in manufacturing processes for a surfaceacoustic wave element, a thermistor, a semiconductor device, and thelike. Particularly, as illustrated in FIG. 1, a circular shape having anorientation flat plane formed therein can be preferably used.

When the shape of the diamond substrate 1 is a circular shape or acircular shape having an orientation flat plane formed therein asillustrated in FIG. 1, the diameter is preferably equal to or greaterthan two inches (about 50.8 mm) from the viewpoint of an increase insize of a practical substrate, more preferably equal to or greater thanthree inches (about 76.2 mm), and still more preferably equal to orgreater than six inches (about 152.4 mm). In consideration ofdimensional tolerance of the diamond substrate 1, in this specification,a diameter range of 49.8 mm, which is obtained by subtracting 1.0 mmcorresponding to 2% of 50.8 mm from two inches, to 50.8 mm is defined tocorrespond to two inches.

The upper limit of the diameter is not particularly limited, but ispreferably equal to or less than eight inches (about 203.2 mm) in termsof practical use. In order to manufacture a lot of elements or devicesat a time, a rectangular diamond substrate having an area equivalent toor greater than the diameter of two inches may be used.

Therefore, the surface 2 of the diamond substrate 1 has at least asurface area of 20 cm². From the viewpoint of an increase in size, thesurface preferably has a surface area of 1297 cm² or less.

The thickness t of the diamond substrate 1 can be set arbitrarily, ispreferably equal to or less than 3.0 mm in terms of a self-supportedsubstrate, and is more preferably equal to or less than 1.5 mm and stillmore preferably equal to or less than 1.0 mm, from the viewpoint of usefor a manufacturing line of elements or devices. On the other hand, thelower limit of the thickness t is not particularly limited, and ispreferably equal to or greater than 0.05 mm and is more preferably equalto or greater than 0.3 mm, from the viewpoint of securing of rigidity ofthe diamond substrate 1 to prevent generation of a fissure, a fracture,or a crack.

Here, the “self-supported substrate” or “self-support substrate” in thepresent invention means a substrate having such strength that is notonly suitable to maintain its own shape and causes no problem inhandling thereof. The thickness t can be preferably set to 0.3 mm ormore to have such strength. Since a diamond is a very hard material, theupper limit of the thickness t as a self-supported substrate ispreferably equal to or less than 3.0 mm in consideration of easiness incleavage after elements or devices are formed or the like. In terms of aself-supported substrate which can be most frequently used for elementsor devices, the thickness t most preferably ranges from 0.5 mm to 0.7 mm(ranges from 500 μm to 700 μm).

Diamond single crystals can be preferably used as the diamond crystalsforming the diamond substrate 1. The diamond single crystals may be anyof an Ia type, an Ia type and an IIb type, and the Ia type can bepreferably used when the diamond substrate 1 is used as a substrate of asemiconductor device, from the viewpoint of a quantity of crystaldefects or distortion, or a magnitude of a full width at half maximum ofan X-ray rocking curve. The diamond substrate 1 is formed from a singlediamond single crystal and coupling boundaries at which plural diamondsingle crystals are coupled are not present on the surface 2.

The surface 2 of the diamond substrate 1 is subjected to lapping,polishing, or chemical mechanical polishing (CMP). On the other hand,the back surface of the diamond substrate 1 is subjected to lappingand/or polishing. The surface 2 is processed mainly for obtaining a flatsubstrate shape and the back surface is processed mainly for obtaining adesired thickness t. Since the surface 2 is desired to have surfaceroughness Ra enough to form elements or devices, the surface roughnessis preferably less than 1 nm and more preferably equal to or less than0.1 nm at which the surface is flattened at an atomic level. The surfaceroughness Ra may be measured using a surface roughness measuringinstrument.

When the diamond substrate 1 is formed of single crystals, the planeorientation of a crystal plane of the surface 2 may be any one of (111),(110), and (100) and is not limited to these plane orientations. Theplane orientation (100) can be preferably used from the viewpoint offormation of elements or devices, growth of diamond single crystals, orthe like.

When the diamond substrate 1 is formed from a single diamond singlecrystal, a coupling boundary at which plural diamond single crystals arecoupled is not present on the surface 2 and thus deterioration incrystal quality at a boundary is prevented. Accordingly, when thediamond substrate 1 is formed from a single diamond single crystal, thefull width at half maximum (FWHM) of an X-ray rocking curve on thesurface 2 (particularly, (100)) can be 300 seconds or less over theentire surface 2.

As described above, in the diamond substrate 1 which is formed from asingle diamond single crystal, a full width at half maximum of the X-rayrocking curve can be realized to be 300 seconds or less and it is thuspossible to provide a diamond substrate 1 with high quality. Inaddition, it is possible to manufacture elements or devices with highquality and high efficiency by using the diamond substrate 1.

A diamond substrate manufacturing method according to the presentinvention will be described below in detail with reference to FIGS. 2 to9. First, a base substrate 4 is prepared as illustrated in FIG. 2. Thematerial of the base substrate 4 is, for example, magnesium oxide (MgO),aluminum oxide (α-Al₂O₃:sapphire), Si, quartz, platinum, iridium, orstrontium titanate (SrTiO₃).

Among these materials, particularly, since an MgO single crystalsubstrate and an aluminum oxide (sapphire) single crystal substrate arevery thermally stable and the substrates with a diameter of eight inches(about 203.2 mm) are provided, the MgO single crystal substrate and thealuminum oxide single crystal substrate can be preferably used as a basesubstrate for growth of a diamond single crystal for the reason of easyavailableness.

At least one side 4 a of the base substrate 4 is mirror-polished. In adiamond layer growing step to be described later, the diamond layer isgrown and formed on the surface (on the surface of the one side 4 a)which is subjected to mirror polishing. A base substrate of which oneside 4 a and a back side 4 b are mirror-polished may be used ifnecessary. In this case, any one surface can be arbitrarily used as adiamond layer growing surface.

The mirror polishing can be performed such that the surface is smoothedto enable a diamond layer to grow on at least the one side 4 a, and canbe preferably performed such that the surface roughness Ra is equal toor less than 10 nm as a reference. When the surface roughness Ra of theone side 4 a is greater than 10 nm, the quality of the diamond layergrowing on the one side 4 a deteriorates. No crack is present on the oneside 4 a. The surface roughness Ra can be measured using a surfaceroughness measuring instrument.

When the MgO single crystal substrate is used as the base substrate 4,the diamond layer growing plane preferably has a plane orientation of(001). Planes other than (001) can also be used.

The shape in the in-plane direction of the base substrate 4 is notparticularly limited and may be, for example, a circular shape or arectangular shape. When the base substrate 4 has a circular shape, thediameter of the base substrate 4 is preferably equal to or greater thantwo inches (about 50.8 mm) from the viewpoint of an increase in size,more preferably equal to or greater than three inches (about 76.2 mm),and still more preferably equal to or greater than six inches (about152.4 mm). The upper limit of the diameter is not particularly limited,and is preferably equal to or less than eight inches in terms ofpractical use. In consideration of dimensional tolerance of the basesubstrate 4, in this specification, a diameter range of 49.8 mm, whichis obtained by subtracting 1.0 mm corresponding to 2% of 50.8 mm fromtwo inches, to 50.8 mm is defined to correspond to two inches.

On the other hand, when the base substrate 4 has a rectangular shape,the size of the base substrate is preferably equal to or greater than 50mm×50 mm and more preferably equal to or greater than 75 mm×75 mm, fromthe viewpoint of an increase in size. The upper limit of the size ispreferably equal to or less than 200 mm×200 mm in terms of practicaluse.

Therefore, the surface of the base substrate 4 has at least a surfacearea of 20 cm². From the viewpoint of an increase in size, the surfacepreferably has a surface area of up to 1297 cm².

The thickness d4 of the base substrate 4 is preferably equal to or lessthan 3.0 mm, more preferably equal to or less than 1.5 mm, and stillmore preferably equal to or less than 1.0 mm. The lower limit of thethickness d4 is not particularly limited, but is preferably equal to orgreater than 0.05 mm and more preferably equal to or greater than 0.4mm, from the viewpoint of securing of rigidity of the base substrate 4.When the shape in the in-plane direction of the base substrate 4 is acircular shape and the diameter thereof ranges from 50 mm to 150 mm, thethickness d4 is preferably equal to or greater than 0.3 mm. When thediameter is greater than 150 mm, the thickness d4 is preferably equal toor greater than 0.6 mm.

After the base substrate 4 is prepared, a diamond layer 9 formed of adiamond single crystal is grown and formed on the one side 4 a asillustrated in FIG. 3. The method of growing the diamond layer 9 is notparticularly limited and a known method can be used. Specific examplesof the growth method include vapor phase growth methods such as a pulselaser deposition (PLD) method and a chemical vapor deposition (CVD)method.

The base substrate 4 is subjected to thermal cleaning before the diamondlayer 9 grows, and then the diamond layer 9 is made to grow. In the PLDmethod, laser sputtering is performed on a target containing graphite,amorphous carbon, or diamond in the atmosphere of gas composedsubstantially of oxygen to cause carbon to fly out of the target and adiamond layer 9 is made to grow on the one side 4 a of the basesubstrate 4. It is preferable that a furnace pressure range from1.33×10⁻⁴ Pa to 133.32 Pa, the temperature of the base substrate 4 rangefrom 300° C. to 1000° C., and the distance between the target and thebase substrate 4 range from 10 mm to 100 mm.

In the CVD method, the base substrate 4 is disposed in a CVD growthfurnace and a CVD diamond single crystal is made to grow on the one side4 a of the base substrate 4. A DC plasma method, a hot filament method,a combustion flame method, an arc jet method, or the like can be used asthe growth method, and the microwave plasma method can be preferablyused to obtain a diamond with high quality in which mixing amount ofimpurities is small.

In epitaxial growth of the diamond layer 9 using the microwave plasmaCVD method, gas containing hydrogen and carbon is used as raw materialgas. Methane as the gas containing hydrogen and carbon is introducedinto the growth furnace at a methane/hydrogen gas flow rate of 0.001% to30%. The furnace pressure is kept at about 1.3×10³ Pa to 1.3×10⁵ Pa andmicrowaves of a frequency of 2.45 GHz (±50 MHz) or 915 MHz (±50 MHz) isapplied with power of 100 W to 60 kW to generate plasma. Active speciesare deposited on the one side 4 a of the base substrate 4 of which thetemperature is kept at 700° C. to 1300° C. by heating of the plasma andCVD diamonds are made to grow.

An iridium (Ir) single crystal film may be formed on the surface of thebase substrate 4 as a pre-treatment before the diamond layer 9 grows,and the diamond layer 9 may be made to grow on the Ir single crystalfilm.

The thickness d9 of the diamond layer 9 illustrated in FIG. 6 is set tothe height of pillar-shaped diamonds to be formed and is preferably setto a thickness of 30 μm to 500 μm.

Plural pillar-shaped diamonds 11 are formed from the diamond layer 9. Inthe formation, the pillar-shaped diamonds 11 can be formed usingetching, photolithography, laser machining, or the like.

Since the diamond layer 9 is formed on the base substrate 4 byheteroepitaxial growth, a lot of crystal defects are formed in thediamond layer 9 but the defects can be thinned out by forming the pluralpillar-shaped diamonds 11.

A diamond substrate layer 12 is grown and formed on the tips of thepillar-shaped diamonds 11. By causing a diamond single crystal to growfrom the tips of the pillar-shaped diamonds 11, a diamond single crystalcan grow uniformly at every pillar-shaped diamond 11. By causing thediamond single crystal to grow in a direction transverse to the heightdirection of the pillar-shaped diamonds 11, coalescence of the diamondsingle crystals grown form the pillar-shaped diamonds 11 can be startedat the same timing.

The diamond substrate layer 12 is manufactured by coalescing the diamondsingle crystals grown from the pillar-shaped diamonds 11. The number ofpillar-shaped diamonds 11 to be formed varies depending on the diameterof the base substrate 4, and the number of pillar-shaped diamonds 11 canincrease with an increase in diameter of the base substrate 4.Accordingly, a diamond substrate layer with a diameter of two inches canbe manufactured from a base substrate with a diameter of two inches, anda diamond substrate layer with a diameter of eight inches can bemanufactured from a base substrate with a diameter of eight inches.

By setting the pitch of the pillar-shaped diamonds 11 to the same gap(pitch) as growing of cores of the diamond single crystals and growingdiamond single crystals from the pillar-shaped diamonds, it is possibleto improve the surface quality of the diamond substrate layer 12 and torealize a full width at half maximum of 300 seconds or less on theentire surface.

By setting the diameter and the pitch of the pillar-shaped diamonds 11to be equal to or less than 10 μm, it is possible to improve the surfacequality of the diamond substrate layer 12 and to realize a full width athalf maximum of 300 seconds or less.

The pitch of the pillar-shaped diamonds 11 can be appropriatelyselected. However, the pitch can be properly selected depending onwhether the coalescence of the diamond single crystals grown from thepillar-shaped diamonds 11 is started at the same timing.

After the diamond substrate layer 12 is formed, the diamond substratelayer 12 is separated from the base substrate 4 at parts of thepillar-shaped diamonds 11. For the purpose of separation at thepillar-shaped diamonds 11, a certain force needs to be applied to theparts of the pillar-shaped diamonds 11. In the present invention, ingrowing of the diamond substrate layer 12, a stress is generated in thepillar-shaped diamonds 11 by a warp generated in the base substrate 4and the diamond substrate layer 12, the pillar-shaped diamonds 11 aredestroyed due to the stress, and the diamond substrate layer 12 isseparated from the base substrate 4.

For example, as illustrated in FIG. 8, the base substrate 4 formed ofMgO single crystals has a thermal expansion coefficient and a latticeconstant larger than those of the diamond substrate layer 12 formed ofdiamond single crystals. Accordingly, in cooling the diamond substratelayer 12 after growth, a tensile stress is generated as indicated by anarrow from the center to the ends on the diamond substrate layer 12side. The tensile stress is a stress which is generated due to adifference in lattice constant between the base substrate 4 and thediamond substrate layer 12 and/or a stress which is generated due to adifference in thermal expansion coefficient between the base substrate 4and the diamond substrate layer 12. As a result, all of the diamondsubstrate layer 12, the base substrate 4, and the pillar-shaped diamonds11 warp greatly such that the diamond substrate layer 12 side is convexas illustrated in FIG. 8.

A large tensile stress is applied to the pillar-shaped diamonds 11 and acrack is formed in the pillar-shaped diamonds 11. As the crack isprogressed, the pillar-shaped diamonds 11 are destroyed as illustratedin FIG. 9 and the diamond substrate layer 12 is separated from the basesubstrate 4.

Even when the stress generated in the diamond substrate layer 12increases with an increase in size of the diamond substrate layer 12,the stress of the diamond substrate layer 12 is released to the outsideby the destruction of the pillar-shaped diamonds 11. Accordingly, it ispossible to prevent a crack from being generated in the diamondsubstrate layer 12 and thus to manufacture a large diamond substrate 1.

By using the stress which is generated due to a difference in latticeconstant between the base substrate 4 and the diamond substrate layer 12and/or the stress which is generated due to a difference in thermalexpansion coefficient between the base substrate 4 and the diamondsubstrate layer 12 for the separation, a device, a mechanism, or a stepfor separation is not particularly necessary after the diamond substratelayer 12 grows. Accordingly, it is possible to simplify the process ofmanufacturing the diamond substrate 1 and to facilitate the separationstep.

It is desired that the height direction of each pillar-shaped diamond 11is set to a direction perpendicular to (001) plane of the diamond singlecrystal forming the diamond layer 9 and the pillar-shaped diamond 11because destruction of the pillar-shaped diamonds 11 due to applicationof a stress can smoothly progress.

The thickness d9 of the diamond layer 9 illustrated in FIG. 6 is set tothe height of the pillar-shaped diamonds to be formed and is preferablyset to a thickness of 30 μm to 500 μm. As illustrated in FIG. 10, thepillar-shaped diamonds 11 may be formed in a state in which a part ofthe diamond layer 9 corresponding to a partial thickness of the lowerpart of the thickness d9 remains.

The aspect ratio of the pillar-shaped diamonds 11 in FIGS. 4 to 10 canbe set to a value at which the pillar-shaped diamonds 11 are not filledfully in growing of the diamond substrate layer 12 and is preferably setto 5 or more.

The cross-sectional shape of the pillar-shaped diamonds 11 may be arectangular shape or a circular shape. However, the pillar-shapeddiamonds 11 need to be rapidly destroyed with application of a stress.In consideration of the above-mentioned description, the cross-sectionalshape of the pillar-shaped diamonds 11 is preferably a circular shape(that is, each pillar-shaped diamond 11 is a cylindrical shape), becausethe stress is uniformly applied in the circumferential direction touniformly destroy the pillar-shaped diamonds 11. Accordingly, sincegeneration of a fissure, a fracture, a crack, or the like in the diamondsubstrate layer 12 due to non-uniform destruction can be prevented, thecircular shape can be more preferably used.

The diameter of each pillar-shaped diamond 11 is preferably set tosubmicron to about 5 μm and the diameter of the central portion of eachpillar-shaped diamond in the height direction is preferably formed to besmaller than the diameter of the tip portion thereof, because thepillar-shaped diamond 11 can be more easily and smoothly destroyed.

After the diamond substrate layer 12 is separated from the basesubstrate 4, the diamond substrate layer 12 is polished to remove theremaining pillar-shaped diamonds 11 and a disk is cut out by slicing andcircular punching. By performing various processes such as lapping,polishing, and CMP and mirror polishing if necessary on the disk, thediamond substrate 1 is manufactured from the diamond substrate layer 12.Accordingly, the thickness d12 of the diamond substrate layer 12 is setto be slightly larger than the thickness t in consideration of apolishing margin. Since the diamond is a material having highesthardness, the polishing margin is preferably set to be as small aspossible from the viewpoint of difficulty in polishing, and can be setto, for example, 50 μm.

By manufacturing the diamond substrate 1 from the diamond substratelayer 12, it is possible to manufacture a large-diameter diamondsubstrate with a diameter of two inches or more. Since the full width athalf maximum of the X-ray rocking curve on the surface 2 of the diamondsubstrate 1 can be realized to be 300 seconds or less over the entiresurface 2, it is possible to provide a diamond substrate 1 with highquality.

EXPLANATION ON REFERENCE NUMERALS

1: diamond substrate

2: surface of diamond substrate

4: base substrate

4 a: one side of base substrate

4 b: back side of base substrate

9: diamond layer

11: pillar-shaped diamond

12: diamond substrate layer

t: thickness of diamond substrate

d4: thickness of base substrate

d9: thickness of diamond layer

d12: thickness of diamond substrate layer

The invention claimed is:
 1. A diamond substrate manufacturing methodcomprising: preparing a base substrate; forming a plurality ofpillar-shaped diamonds formed of diamond single crystals on one side ofthe base substrate; causing a diamond single crystal to grow from a tipof each pillar-shaped diamond and coalescing the diamond single crystalsgrown from the tips of the pillar-shaped diamonds to form a diamondsubstrate layer; separating the diamond substrate layer from the basesubstrate; and manufacturing a diamond substrate from the diamondsubstrate layer, wherein a shape in an in-plane direction of the diamondsubstrate is a circular shape or a circular shape having an orientationflat plane formed therein and has a diameter of two inches or more. 2.The diamond substrate manufacturing method according to claim 1, whereinthe separating of the diamond substrate layer from the base substrate isperformed by generating a stress in the pillar-shaped diamonds anddestroying the pillar-shaped diamonds.
 3. The diamond substratemanufacturing method according to claim 2, wherein the stress is astress generated due to a difference in lattice constant between thebase substrate and the diamond substrate layer and/or a stress generateddue to a difference in thermal expansion coefficient between the basesubstrate and the diamond substrate layer.
 4. The diamond substratemanufacturing method according to claim 1, wherein an aspect ratio ofeach pillar-shaped diamond is equal to or more than five.
 5. The diamondsubstrate manufacturing method according to claim 1, wherein a diameterand a pitch of the pillar-shaped diamonds are set to 10 p.m or less. 6.The diamond substrate manufacturing method according to claim 1, whereinsurface roughness Ra of the one side of the base substrate is equal toor less than 10 nm.
 7. The diamond substrate manufacturing methodaccording to claim 1, wherein a height direction of the pillar-shapeddiamonds is set to a direction perpendicular to (001) plane of diamondsingle crystals forming the pillar-shaped diamonds.
 8. The diamondsubstrate manufacturing method according to claim 1, wherein eachpillar-shaped diamond has a cylindrical shape, and a diameter of acentral portion of each pillar-shaped diamond in the height direction issmaller than a diameter of a tip portion thereof.
 9. The diamondsubstrate manufacturing method according to claim 1, wherein thediameter ranges from two inches to eight inches.